Vehicles including automobiles are provided at different portions thereof with doors, a trunk lid, a back door and other opening/dosing members that are attached to the vehicle by way of hinges. Particularly, many vans and station wagons are provided with a back door at the outer end of the vehicle for the ease of access when loading and unloading cargoes.
Normally, such a back door is attached to the vehicle by way of hinges that are rigidly secured to the rear end of the roof of the vehicle to allow the door to turn around an axis of rotation that is substantially horizontal so as to allow the back door swing up and down around the hinges. The back door is also referred to as lift gate or rear hatch because it swings fully upward from the vehicle body when it is operated.
Since back doors are mostly large and heavy, women and children often feel it difficult to open and close the back door. Particularly, since the back door swings fully upward when it is operated, it may be highly difficult for women and children to open and close it.
Under the current circumstances where station wagons and other cars for family use are increasing, some vehicles are provided with an automatic opening/closing apparatus for automatically opening/closing the back door so as to allow women and children to open and close it without difficulty. Since such an automatic opening/dosing apparatus can be remotely controlled from the driver's seat to open and dose the back door, there is a considerable demand for such automatic opening/dosing apparatuses to be attached to vehicles because of the convenience they provide.
As known automatic opening/dosing apparatuses, for example, as shown in Japanese Patent Application Laid-Open Publication No. 2001-280000, an actuator unit that is typically driven to operate by an electric motor or the like is arranged in the roof of a vehicle and the force output from the actuator unit is transmitted to the back door by way of a link mechanism to open and dose a back door. The actuator unit is of the so-called rack and pinion type and force is output from the electric motor to realize a linear reciprocating motion of the rack by way of the pinion. The rack can freely swing around the rotary axis of the pinion relative to the vehicle and move along a direction inclined relative to the vertical direction of the vehicle. On the other hand, a link arm that is curved around the pivot of the hinge is rigidly secured to the back door at an end thereof and the rack is linked to the other end of the link arm by means of a coupling pin. As the electric motor is driven, the linear reciprocating motion of the rack is converted into an opening/closing motion of the back door by way of the link arm, so that the back door is opened and closed.
However, of such an opening/closing apparatus, the link arm is rigidly secured to the back door so that the load of the back door when being opened or dosed is concentratively applied to the base part of the link arm so that the link arm has to be rigidly secured to the back door to show an enhanced strength. There has been proposed an arrangement where the link arm is coupled to the back door in such a way that it can swing freely to prevent the load from being concentratively applied to the base part of the link arm, thereby avoiding the above identified problem. With this arrangement, since the link arm can freely swing relative to the vehicle in addition to the rack, the link arm has to be supported so as to make it to be directed in a predetermined direction that can vary depending on the direction along which the door is being opened or closed in order to convert the linear reciprocating motion of the rack into an opening/closing motion of the back door by way of the link arm.
Although not publicly known, there is a technique of arranging a pair of support members arranged opposite to each other with the link arm interposed between them at the side of the actuator unit and another pair of support members arranged opposite to each other with the link arm interposed between them at the side of the back door so that the link arm may be moved to open and close the back door by means of the support members. Sliders, rollers or the like that can slide relative to the link arm are used as support members so that the load applied to the link arm is borne by selected ones of the support members depending on the direction of application of the load to consequently define the direction of application of the force being applied to the link arm by the rack and move the link arm to open and close the back door.